The invention relates to an implant with a coupling. More particularly, the invention relates to osteosynthesis implants with couplings having gimbal-type swivel joints.
Angularly fixed longitudinal supports such as plates and bars increasingly are used in osteosynthesis applications. Such devices are particularly useful for treating fractures that are located near joints, or for anchoring screws in the spinal column. In applications that use short screws, the screws typically can be inserted in the longitudinal support at a preset angle without presenting problems. When longer screws are necessary, a fixed, system-dependent orientation of the screw may be impractical or unwieldy.
To facilitate the use of longer screws in regions such as the spine, special ball joints have been developed. In addition, as disclosed in German patent DE 195 48 395, bone plates have been proposed with specially configured screw holes drilled therein for accepting correspondingly shaped screw heads. The bone screw thus may be locked in place in the bone plate in a relatively randomly selectable orientation. But, the complexity, bulky nature, and insufficient strength provided by the connections of these ball joints and screw head-borehole configurations does not sufficiently remedy the inherent problems encountered with fixed, system-dependent orientations of screws.
Also disclosed in German patent DE 24 38 669 to Bezold is an osteosynthesis bone plate with screw holes having a respective spacing that can be manipulated using externally generated forces. The screw holes are arranged in the form of lugs punched out of the main body of the osteosynthesis plate and connected thereto merely by elastic legs. In one embodiment, the legs are aligned along one axis and connected to the lug diametrically relative to the axis. When the lug is lifted out of the plane of the plate, the legs are bent such that the rotational axis of the lug no longer coincides with the vertical axis of either the lug itself or the screw hole. Use in clinical applications thus is limited because as the lug is turned, the center of the screw hole is undesirably shifted.
There exists a need for a bone plate with a coupling that facilitates the use of a wide range of sizes of bone screws. There further exists a need for a coupling that requires less space than ball joints and provides simplicity in design and use. Additionally, there is a need for a substantially flat swivel joint for use in connecting implant components such as a bone screw and a bone plate.
The present invention provides an implant and coupling capable of furnishing these improvements, and advantageously has application in a wide range of other implants unrelated to bone screw support.
The present invention relates to an osteosynthesis implant that includes a coupling comprising at least one annular element having a pair of connecting members for coupling the annular element to a surrounding structure. The connecting members provide the annular element with a swiveling motion with respect to the surrounding structure for alignment of the annular element during insertion or implantation of the implant. The connecting members also form a single coupling axis with the surrounding structure and the annular element swivels about that coupling axis.
In one embodiment, the annular element defines a hole for receiving a fastener and the surrounding structure is the implant. Typically, the annular element has a generally circular configuration and defines a generally cylindrical hole that extends along a central axis. Also, the hole is generally perpendicular to at least one of the top and bottom surfaces of the annular element.
In another embodiment, the annular element has a top surface, a bottom surface, and a first thickness defined between the top and bottom surfaces, and the implant has a top implant surface, a bottom implant surface, and a second thickness defined between the top and bottom implant surfaces and the connecting members have a connection thickness. Typically, the first thickness of the annular element is less than or equal to the second thickness of the implant and the connection thickness of the connecting members is also less than or equal to the second thickness of the implant.
In another embodiment, the coupling has inner and outer annular elements where each element has a pair of connecting members and the connecting members of the inner annular element are coupled to the outer annular element and the connecting members of the outer annular element are coupled to a surrounding structure. This permits the inner annular element to be provided with a first swiveling motion and the outer annular element to be provided with a second swiveling motion. Also, the connecting members of the inner annular element form a first coupling axis and the connecting members of the outer annular element form a second coupling axis that is positioned at an angle with respect to the first coupling axis. The first and second coupling axes can be substantially perpendicular to each other.
In another embodiment of the present invention, the inner and outer annular elements, the connecting members and the implant are all formed of unitary construction and each connecting member is capable of exhibiting elastic deformation to permit the annular element to swivel.
In another embodiment, the implant is an intervertebral element having at least one surface that includes the surrounding structure in which the inner and outer annular elements are disposed so that more precise alignment can be provided. In an exemplary embodiment, the intervertebral element has two parallel surfaces, each of which provides the surrounding structure in which the inner and outer annular elements are disposed. The two parallel surfaces define a central longitudinal axis and the intervertebral element has a first through-hole extending generally perpendicular to the central longitudinal axis and has a second through-hole extending generally perpendicular to the first through-hole.
In another exemplary embodiment, the intervertebral element has top and bottom surfaces, each of which provide the surrounding structure in which inner and outer annular elements are disposed. In addition, the top and bottom surfaces are, typically, configured as generally oval plates and are spaced apart from each other with a central connector that is generally cylindrical. Furthermore, the central connector is fixed to the inner annular elements, such that swivelling of the plates is permitted while the inner annular elements remain parallel to each other and the connecting members of the inner annular element form a first coupling axis and the connecting members of the outer annular element form a second coupling axis that is generally perpendicular to the first coupling axis. Typically, the implant is configured and dimensioned to be received between two vertebral bodies.
In another embodiment of the present invention, the surrounding structure in which inner and outer annular elements are disposed is a fixation system for a longitudinal support. The fixation system comprises a mounting head having a top surface and bottom surface, a first head bore which extends from the top head surface to the bottom head surface about a head bore longitudinal axis and a second head bore which extends substantially perpendicular to the first head bore. The second head bore is configured and dimensioned to receive a longitudinal support and the inner annular element includes a hole for a pedicle screw.